1. Field of the Invention
The present invention relates to a power transmission mechanism of power-driven rotary tools such as drills and screwdrivers, and more particularly to a power transmission mechanism for imparting reciprocating movement as well as rotation.
2. Description of the Related Art
Power-driven drills, screwdrivers, and other rotary tools have a mechanism for transmitting power from a driving mechanism to a rotary output shaft. Examples of such transmission mechanisms include: a clutch cam arrangement being axially movable via a pin inserted through a transmission shaft in a direction perpendicular to its axis as disclosed in Japanese Utility Model Laying-Open Gazette No. Sho-63-30476; and another clutch cam arrangement being axially movable via a spline mounted on a rotary output shaft as disclosed in Japanese Utility Model Laying-Open Gazette No. Hei-2-56512.
A power-driven combination drill and screwdriver having a clutch arrangement is also known as disclosed in U.S. Pat. Nos. 4,161,242 and 4,823,885.
Conventional power-driven rotary tools including the combination tool mentioned above, however, do not have function of reciprocation; that is, the transmission shaft and the output shaft are not axially movable. Another vibration drill is thus required for making holes in bricks or concrete.
When an impact mechanism for imparting axial reciprocation to the output shaft is mounted on the power-driven rotary tool to move the output shaft along the axis, reciprocation of the output shaft further moves the clutch cam relative to the output shaft and thereby causes untimely abrasion and wear of the clutch cam. Namely, the sliding friction undesirably shortens the life of the power transmission mechanism. Frictional resistance also prevents smooth reciprocating movement of the output shaft. Especially in a battery-powered tool, the loading badly consumes the battery and shortens the possible life thereof.